1. Field of the Invention
The present disclosure generally relates to systems and methods for three-dimensional surface feature measurements. More particularly, the disclosure generally relates to portable pavement surface measurement device.
2. Description of the Relevant Art
The three-dimensional (3D) surface measurement devices or scanners are widely used to measure three-dimensional structures of an object or a surface. The 3D surface structures are used to measure surface features, build 3D models, or create a mechanical drawing used for reverse engineering. Different techniques exist for the design and implementation of such 3D scanners. One method uses a point or line distance sensor and a mechanical stage. Usually, the stage moves the sensor in one or two directions on a surface area. The sensor measures the distance between a reference surface and the object surface. As the sensor is moved at a fixed elevation, changes of measured distances are used to generate an image or map of the scanned surface. This mechanical scanning technology requires a very precise conveyance mechanism to achieve acceptable precision and accuracy. Thus this technology is often considered as cost-ineffective as well as inefficient due to the speed at which data is gathered.
Most current 3D scanning devices use a non-contact optical sensor (e.g., laser triangulation sensor). Laser triangulation is a concept in which the positions of a reflected laser light from a surface are captured in a photo detector as a function of the distance between the surface and the photo detector. The sensor typically is either a point type having a point laser source and a linear array of photo detector measuring a single point from a surface, or a line type having a laser line projector and an area array (e.g., a camera), and measures a line from a surface. The laser light may appear in multiple units (pixels) of the photo detector. Different processes are used to determine the center of the laser light to represent measured distance. For example, the center of gravity method detects laser light position in sub-pixel resolution. The measured laser light position could be one fourth, one sixteenth, or even one sixty-fourth of the photo detector pixel size.
Other current methods of 3D measurement include the stereo-vision or stereo-match technology. Two identical imaging devices (e.g., cameras) are positioned in well defined locations. The imaging devices obtain images of the target object from different positions at different angles. A particular feature on a target object will appear at different pixel positions in images from the two devices. The geometric location of the surface feature can be calculated using the two pixel positions and other parameters such as device location and directions. For a complete measurement, all pixels in images from the two image devices that correspond to the same features need to be identified. However, it is often difficult to obtain perfect pixel level feature matching, especially in surfaces with low color contrast, or surfaces that lack identifying physical features. In the more problematic cases, a pattern projector may be used to create artificial color patterns on the surface. These color patterns, when captured by both imaging devices, can be used to improve the speed and accuracy of the pixel matching processes. Compared to the laser triangulation method, stereo-matching method is faster. However, the laser triangulation method's resolution is lower and its data noise is higher due to the difficulty of pixel matching.
Therefore a system and/or method which provides a better automated test for a more accurate measurement of pavement texture and other features would be highly desirable.